Zoom lens system, interchangeable lens apparatus and camera system

ABSTRACT

Provided is a zoom lens system including a compact focusing lens unit and having a suppressed change in image magnification at the time of movement of the focusing lens unit. The zoom lens system of the present invention includes, in order from object side to image side, a first lens unit G 1  having positive optical power, a second lens unit G 2  having negative optical power, a third lens unit G 3  having negative optical power, and a fourth lens unit G 4  having positive optical power. An aperture diaphragm A is arranged on the object side adjacent to the fourth lens unit G 4 . Further, the fourth lens unit G 4  includes, in order from object side to image side, a lens element L 8  having positive optical power, a lens element L 9  having positive optical power, and a lens element L 10  having negative optical power.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application Nos.2009-020092 and 2009-020093 filed on Jan. 30, 2009. Hereby, the contentsof Japanese Patent Application Nos. 2009-020092 and 2009-020093 areincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens system and, in particular,to a zoom lens system suitable for an imaging lens system employed in aninterchangeable lens apparatus in a so-called interchangeable-lens typedigital camera system. Further, the present invention relates to aninterchangeable lens apparatus and a camera system that employ this zoomlens system.

2. Description of the Background Art

In recent years, interchangeable-lens type digital cameras are rapidlyspreading. The interchangeable-lens type digital camera is a camerasystem including: a camera body employing an image sensor composed of aCCD (Charge Coupled Device), a CMOS (Complementary Metal-OxideSemiconductor), or the like; and an interchangeable lens apparatusemploying an imaging lens system for forming an optical image on thelight acceptance surface of the image sensor. Zoom lens systemsapplicable to the above interchangeable-lens type digital camera aredisclosed in Japanese Laid-Open Patent Publication No. 2005-284097,Japanese Laid-Open Patent Publication No. 2005-352057, JapaneseLaid-Open Patent Publication No. 2006-221092, Japanese Laid-Open PatentPublication No. 2005-316396, Japanese Laid-Open Patent Publication No.2006-267425, Japanese Laid-Open Patent Publication No. 2007-219315,Japanese Laid-Open Patent Publication No. 2008-3195, and JapaneseLaid-Open Patent Publication No. 2008-15251.

On the other hand, there are interchangeable-lens type digital camerasemploying a function of displaying image data generated by the imaginglens system or the image sensor on a display unit such as a liquidcrystal display or the like of a camera body (hereinafter referred to as“live view function”) (e.g., Japanese Laid-Open Patent Publication No.2000-111789 and Japanese Laid-Open Patent Publication No. 2000-333064).

SUMMARY OF THE INVENTION

In the interchangeable-lens type digital cameras disclosed in JapaneseLaid-Open Patent Publication No. 2000-111789 and Japanese Laid-OpenPatent Publication No. 2000-333064, when the live view function is beingperformed, a contrast AF method is employed to perform focusingoperation. The contrast AF is the focusing operation based on thecontrast value of image data obtained from the image sensor.Hereinafter, an operation of the contrast AF will be described.

First, the interchangeable-lens type digital camera oscillates thefocusing lens unit in the optical axis direction at a high-speed(hereinafter referred to as “wobbling”) thereby to detect the directionof displacement from an in-focus condition. After the wobbling, theinterchangeable-lens type digital camera detects, from an output signalof the image sensor, signal components in a predetermined frequency bandin an image region and calculates an optimal position of the focusinglens unit for realizing the in-focus condition. Thereafter, theinterchangeable-lens type digital camera moves the focusing lens unit tothe optimal position, and completes the focusing operation. When thefocusing operation is performed continuously in video image taking orthe like, the interchangeable-lens type digital camera repeats a seriesof the above operations.

Generally, in order that uneasiness such as flickers should be avoided,video displaying need be performed at a high rate of, for example, 30frames per second. Thus, basically, video image taking using theinterchangeable-lens type digital camera also need be performed at thesame rate of 30 frames per second. Accordingly, the focusing lens unitneed be driven at the high rate of 30 Hz at the time of wobbling.

However, if the weight of the focusing lens unit is large, a largermotor or actuator is required to move the focusing lens unit at a highrate. This causes a problem that the outer diameter of the lens barrelis increased. However, in the case of the zoom lens systems for theinterchangeable-lens type digital camera disclosed in the aboveconventional arts, the focusing lens unit is hardly light-weighted.

Further, in the interchangeable-lens type digital camera, it should benoted that the size of the image corresponding to a photographic objectvaries in association with wobbling. This variation in the image iscaused mainly by the fact that the movement of the focusing lens unit inthe optical axis direction generates a change in the focal length of theentire lens system. Then, when a large change in the image takingmagnification is generated in association with wobbling, the imagetaking person will feel uneasiness.

An object of the present invention is to provide a zoom lens systemwhich includes a compactly constructed focusing lens unit and which hasa suppressed change in the image magnification at the time of movementof the focusing lens unit, and an interchangeable lens apparatus and acamera system which employ this zoom lens system.

A zoom lens system according to the present invention includes aplurality of lens units and an aperture diaphragm arranged in the lensunits and performs zooming by changing intervals among the lens units.The plurality of lens units, in order from an object side to an imageside, includes: a first lens unit having positive optical power; asecond lens unit having negative optical power; a third lens unit havingnegative optical power; and a fourth lens unit having positive opticalpower. The aperture diaphragm is arranged on the object side relative tothe fourth lens unit so as to be adjacent to the fourth lens unit. Thefourth lens unit includes, in order from the object side to the imageside, a lens element having positive optical power, a lens elementhaving positive optical power, and a lens element having negativeoptical power.

Further, another zoom lens system according to the present inventionincludes a plurality of lens units and performs zooming by changingintervals among the lens units. The plurality of lens units, in orderfrom an object side to an image side, includes: a first lens unit havingpositive optical power: a second lens unit having negative opticalpower; a third lens unit having negative optical power; and a fourthlens unit having positive optical power. The fourth lens unit includes,in order from the image side to the object side, a lens element havingpositive optical power, a lens element having negative optical power, alens element having negative optical power, and a lens element havingpositive optical power.

Further, an interchangeable lens apparatus according to the presentinvention includes: any of the above zoom lens systems; and a mountsection detachably connected to a camera body that includes an imagesensor which receives an optical image formed by the zoom lens systemthereby to convert the optical image to an electrical image signal.

Moreover, a camera system according to the present invention includes:an interchangeable lens apparatus including any of the above zoom lenssystems; and a camera body which is connected to the interchangeablelens apparatus via a camera mount section in an attachable and removablemanner and includes an image sensor which receives an optical imageformed by the zoom lens system thereby to convert the optical image toan electrical image signal.

According to the present invention, it is possible to provide a zoomlens system which includes a compactly constructed focusing lens unitand which has a suppressed change in image magnification at the time ofmovement of the focusing lens unit, and an interchangeable lensapparatus and a camera system which employ the zoom lens system.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 1 (Example 1);

FIG. 2 is a longitudinal aberration diagram showing an infinity in-focuscondition of a zoom lens system according to Example 1;

FIG. 3 is a lateral aberration diagram in a basic state where image blurcompensation is not performed and in an image blur compensation state ata telephoto limit of a zoom lens system according to Example 1;

FIG. 4 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 2 (Example 2);

FIG. 5 is a longitudinal aberration diagram showing an infinity in-focuscondition of a zoom lens system according to Example 2;

FIG. 6 is a lateral aberration diagram in a basic state where image blurcompensation is not performed and in an image blur compensation state ata telephoto limit of a zoom lens system according to Example 2;

FIG. 7 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 3 (Example 3);

FIG. 8 is a longitudinal aberration diagram showing an infinity in-focuscondition of a zoom lens system according to Example 3;

FIG. 9 is a lateral aberration diagram in a basic state where image blurcompensation is not performed and in an image blur compensation state ata telephoto limit of a zoom lens system according to Example 3;

FIG. 10 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 4 (Example 4);

FIG. 11 is a longitudinal aberration diagram showing an infinityin-focus condition of a zoom lens system according to Example 4;

FIG. 12 is a lateral aberration diagram in a basic state where imageblur compensation is not performed and in an image blur compensationstate at a telephoto limit of a zoom lens system according to Example 4;

FIG. 13 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 5 (Example 5);

FIG. 14 is a longitudinal aberration diagram showing an infinityin-focus condition of a zoom lens system according to Example 5;

FIG. 15 is a lateral aberration diagram in a basic state where imageblur compensation is not performed and in an image blur compensationstate at a telephoto limit of a zoom lens system according to Example 5;

FIG. 16 is a lens arrangement diagram showing an infinity in-focuscondition of a zoom lens system according to Embodiment 6 (Example 6);

FIG. 17 is a longitudinal aberration diagram showing an infinityin-focus condition of a zoom lens system according to Example 6;

FIG. 18 is a lateral aberration diagram in a basic state where imageblur compensation is not performed and in an image blur compensationstate at a telephoto limit of a zoom lens system according to Example 6;and

FIG. 19 is a schematic construction diagram of a camera system accordingto Embodiment 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1, 4, 7, 10, 13, and 16 show lens arrangement diagrams of zoomlens systems according to Embodiments 1, 2, 3, 4, 5, and 6,respectively, and each show a zoom lens system in a infinity in-focuscondition.

In each diagram, part (a) shows a lens configuration at a wide-anglelimit (in the minimum focal length condition: focal length f_(W)), part(b) shows a lens configuration at a middle position (in an intermediatefocal length condition: focal length f_(M)=√(f_(W)*f_(T))), and part (c)shows a lens configuration at a telephoto limit (in the maximum focallength condition: focal length f_(T)). Further, in each diagram, eachbend arrow located between part (a) and part (b) indicates a lineobtained by connecting the positions of the lens units respectively at awide-angle limit, a middle position, and a telephoto limit, in orderfrom the top. In the part between the wide-angle limit and the middleposition, and the part between the middle position and the telephotolimit, the positions are connected simply with a straight line, andhence this line does not indicate actual motion of each lens unit.Moreover, in each diagram, an arrow imparted to a lens unit indicatesfocusing from an infinity in-focus condition to a close-object in-focuscondition. That is, the arrow indicates the moving direction at the timeof focusing from an infinity in-focus condition to a close-objectin-focus condition.

In FIGS. 1, 4, 7, 10, 13, and 16, an asterisk “*” imparted to aparticular surface indicates that the surface is aspheric. Further, ineach diagram, symbol (+) or symbol (−) imparted to the symbol of eachlens unit corresponds to the sign of the optical power of the lens unit.Still further, in each diagram, the straight line located on the mostright-hand side indicates the position of the image surface S. On theobject side relative to the image surface S (between the image surface Sand a surface of a lens closest to the image side in the fourth lensunit G4), there is arranged a parallel plate P which corresponds to anoptical low-pass filter, a face plate of an image sensor, or the like.Further, in each diagram, an aperture diaphragm A is arranged on theobject side relative to the fourth lens unit G4 while an interval whichdoes not change at the time of zooming is arranged therebetween.

Embodiments 1 to 6

The zoom lens system according to each of Embodiments 1 to 6, in orderfrom the object side to the image side, includes a first lens unit G1having positive optical power, a second lens unit G2 having negativeoptical power, a third lens unit G3 having negative optical power, and afourth lens unit G4 having positive optical power.

The first lens unit G1, in order from the object side to the image side,includes: a negative meniscus first lens element L1 with the convexsurface facing the object side; a bi-convex second lens element L2; anda positive meniscus third lens element L3 with the convex surface facingthe object side. The first lens element L1 and the second lens elementL2 are cemented with each other.

The second lens unit G2, in order from the object side to the imageside, includes: a negative meniscus fourth lens element L4 with theconvex surface facing the object side; a negative meniscus fifth lenselement L5 with the convex surface facing the image side; and abi-convex sixth lens element L6. The fourth lens element L4 is a hybridlens obtained by cementing a transparent resin layer formed of a UVcured resin onto a surface of the lens element facing the object side.The hybrid lens has an aspheric surface formed of a transparent resinlayer. Accordingly, it is possible to form a large diameter asphericsurface which is difficult to obtain by only press-molding of glass.Further, as compared to the case where the lens element is formed of aresin only, the hybrid lens is stable against temperature variation interms of both refractive-index variation and shape variation, and thusit is possible to provide a lens element having a high refractive index.

The third lens unit G3 includes: a bi-concave seventh lens element L7.Both surfaces of the seventh lens element L7 are aspheric.

The fourth lens unit G4, in order from the object side to the imageside; includes: a bi-convex eighth lens element L8; a bi-convex ninthlens element L9; a bi-concave tenth lens element L10; a bi-convexeleventh lens element L11, a bi-convex twelfth lens element L12; abi-concave thirteenth lens element L13; a bi-convex fourteenth lenselement L14; a negative meniscus fifteenth lens element L15 with theconvex surface facing the image side; a negative meniscus sixteenth lenselement L16 with the convex surface facing the image side; and abi-convex seventeenth lens element L17. The ninth lens element L9 andthe tenth lens element L10 are cemented with each other. The twelfthlens element L12 and the thirteenth lens element L13 are cemented witheach other. Moreover, the fourteenth lens element L14 and the fifteenthlens element L15 are cemented with each other. Further, both surfaces ofthe eighth lens element L8 and a surface of the eleventh lens elementL11 facing the image side are aspheric.

The zoom lens system according to each of the embodiments changesintervals among respective lens units at the time of zooming such that:the interval between the first lens unit G1 and the second lens unit G2is made longer at a telephoto limit than the interval at a wide-anglelimit; the interval between the second lens unit G2 and the third lensunit G3 is made longer at a telephoto limit than the interval at awide-angle limit; and the interval between the third lens unit G3 andthe fourth lens unit G4 is made longer at a telephoto limit than theinterval at a wide-angle limit.

More specifically, in Embodiments 1 to 4 and 6, at the time of zoomingfrom a wide-angle limit to a telephoto limit, the individual lens unitsmove in a direction along the optical axis monotonously to the objectside such that: the interval between the first lens unit G1 and thesecond lens unit G2, and the interval between the second lens unit G2and the third lens unit G3 are increased, respectively; whereas theinterval between the third lens unit G3 and the fourth lens unit G4 isdecreased. In Embodiment 5, at the time of zooming from a wide-anglelimit to a telephoto limit, the individual lens units move along theoptical axis monotonously to the object side such that: the intervalbetween the first lens unit G1 and the second lens unit G2 is increased;the interval between the second lens unit G2 and the third lens unit G3is decreased and then increased; and the interval between the third lensunit G3 and the fourth lens unit G4 is decreased. It is noted that inany of the embodiments, the aperture diaphragm A moves to the objectside together with the fourth lens unit G4.

Further, at the time of focusing from an infinity in-focus condition toa close-point in-focus condition, the third lens unit G3 moves to theobject side along the optical axis.

To allow video taking, the focusing lens unit need have high-speedresponse while wobbling operation. In the zoom lens system according toeach of the above Embodiments 1 to 6, the third lens unit G3 is composedof one lens element, whereby a focusing lens unit having a reducedweight and high-speed response is realized. It is noted that thefocusing lens unit need not necessarily be formed of one lens element.If the torque performance of the actuator allows, the focusing lens unitmay includes two lens elements. Further, in order to minimizefluctuation in performance in focusing from infinity to a close-pointdistance, the focusing lens unit has an aspheric surface. The asphericsurface may be a hybrid aspheric surface.

In the zoom lens system according to Embodiments 1 to 6, the fourth lensunit G4 is arranged closest to the object side, and includes: a firstsub lens unit having positive optical power; a second sub lens unithaving negative optical power and arranged on the image side relative tothe first sub lens unit; and a third sub lens unit having positiveoptical power and arranged closest to the image side. It is noted thatthe sub lens unit represents, when one lens unit includes a plurality oflens elements, any one of lens elements or a combination of adjoininglens elements included in the lens unit.

More specifically, in Embodiments 1 to 6, in the fourth lens unit G4,the eighth lens element L8, the ninth lens element L9, the tenth lenselement L10, and the eleventh lens element L11 form a first sub lensunit, and the twelfth lens element L12 and the thirteenth lens elementL13 form a second sub lens unit. Further, the fourteenth lens elementL14, the fifteenth lens element L15, the sixteenth lens element L16, andthe seventeenth lens element L17 form a third sub lens unit.

At the time of image blur compensation for compensating image blurcaused by vibration applied to the zoom lens, the first sub lens unit orthe second sub lens unit moves in a direction perpendicular to theoptical axis. More specifically, in Embodiments 1 to 3, 5, and 6, thesecond sub lens unit moves in a direction perpendicular to the opticalaxis to compensate the movement of an image point caused by vibrationapplied to the entire system, whereas in Embodiment 4, the first sublens unit moves in a direction perpendicular to the optical axis tocompensate the movement of an image point caused by vibration applied tothe entire system.

To obtain an sufficient optical image blur compensation effect, the sublens unit moving in a direction perpendicular to the optical axis needhave high-speed response. In above Embodiments 1 to 3, 5, and 6, thesecond sub lens unit for compensating the movement of an image point isformed of two lens elements, whereby the sub lens unit having a reducedweight and high-speed response is realized. When the sub lens unit forimage blur compensation is formed of two lens elements, it is possibleto suppress, to an allowable range, field curvature aberration orchromatic aberration which is generated at the time of image blurcompensation at the image height in a diagonal direction on the imagesurface, and consequently it is possible to obtain desired imagingcharacteristics. It is noted, however, that the configuration of the sublens unit for image blur compensation varies depending on thecharacteristics required for the zoom lens system. When the allowablerange of the field curvature aberration or chromatic aberration isbroad, the sub lens unit for image blur compensation may be formed ofone lens element.

The following description is given for conditions to be satisfied by thezoom lens system according to each embodiment. Here, in the zoom lenssystem according to each embodiment, a plurality of conditions to besatisfied are set forth. Thus, a configuration of the zoom lens systemthat satisfies as many applicable conditions as possible is mostpreferable. However, when an individual condition is satisfied, a zoomlens system having a corresponding effect can be obtained.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

0.6<f _(4A) /f _(4α)<1.0  (1)

where,

f_(4A) is a focal length of the first sub lens unit in the case wherethe fourth lens unit includes the first sub lens unit having positiveoptical power and the second sub lens unit arranged on the image siderelative to the first sub lens unit and having negative optical power,and

L_(4α) is a composite focal length of the fourth lens unit and a lensunit subsequent thereto at a wide-angle limit.

The condition (1) sets forth the ratio between the focal length of thefirst sub lens unit included in the fourth lens unit and the compositefocal length of the fourth lens unit and a lens unit subsequent thereto.When the value exceeds the upper limit of the condition (1), the fieldcurvature at a wide-angle limit becomes excessive toward the under side.Thus, this situation is unpreferable. On the other hand, when the valuegoes below the lower limit of the condition (1), the back focus iselongated, and thus the overall length cannot be compact.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

0.6<f _(4Ob) /f _(4α)<1.0  (2)

where,

when the fourth lens unit, in order from the object side to the imageside, includes: a lens element having positive optical power; a lenselement having positive optical power; a lens element having negativeoptical power; and a lens element having positive optical power, f_(4Ob)is a composite focal length of the four lens elements, and

f_(4α) is a composite focal length of the fourth lens unit and a lensunit subsequent thereto at a wide-angle limit.

The condition (2) sets forth the ratio between the composite focallength of four lens elements arranged closest to the object side in thefourth lens unit and the composite focal length of the fourth lens unitand a lens unit subsequent thereto. When the value exceeds the upperlimit of the condition (2), the field curvature at a wide-angle limitbecomes excessive toward the under side. When the value goes below thelower limit of the condition (2), the back focus is elongated, and theoverall length cannot be compact.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

−1.5<f _(4B) /f _(4α)<−0.9  (3)

where,

f_(4B) is a focal length of the second sub lens unit in the case wherethe fourth lens unit includes the first sub lens unit having positiveoptical power, and the second sub lens unit arranged on the image siderelative to the first sub lens unit and having negative optical power,and

f_(4α) is a composite focal length of the fourth lens unit and a lensunit subsequent thereto at a wide-angle limit.

The condition (3) sets forth the ratio between the focal length of thesecond sub lens unit included in the fourth lens unit and the compositefocal length of the fourth lens unit and a lens unit subsequent thereto.In the case where the second sub lens unit is moved in a directionperpendicular to the optical axis for the purpose of image blurcompensation, when the value exceeds the upper limit of the condition(3), the amount of blur compensation increases, which leads to upsizingof a blur compensation mechanism. Thus, this situation is unpreferable.In contrast, when the value goes below the lower limit of the condition(3), sensitivity at the time of blur compensation increases, and itbecomes difficult to maintain accuracy of the position control requiredfor blur compensation. Thus, this situation is unpreferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

3.0<f _(4Im) /f _(4α)<4.5  (4)

where,

when the fourth lens unit, in order from the image side to the objectside, includes; a lens element having positive optical power; a lenselement having negative optical power; a lens element having negativeoptical power; and a lens element having positive optical power, f_(4Im)is a composite focal length of the four lens elements; and

f_(4α) is a composite focal length of the fourth lens unit and a lensunit subsequent thereto at a wide-angle limit.

The condition (4) sets forth the ratio between the composite focallength of four lens elements arranged closest to the object side in thefourth lens unit and the composite focal length of the fourth lens unitand a lens unit subsequent thereto. When the value exceeds the upperlimit of the condition (4), the distortion at a wide-angle limit becomesexcessive toward the over side. Thus, this situation is unpreferable.Further, the value goes below the lower limit of the condition (4), theback focus is elongated, and the overall length cannot be compact.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

1.0<f _(4α) /f _(W)<1.5  (5)

where,

f_(4α) is a composite focal length of the fourth lens unit and a lensunit subsequent thereto at a wide-angle limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (5) sets forth the focal length of the fourth lens unitand a lens unit subsequent thereto. When the value exceeds the upperlimit of the condition (5), the incident angle relative to the imagesurface is increased, and it becomes difficult to secure thetelecentricity. Further, when the value goes below the lower limit ofthe condition (5), it is not desirable since the flange back cannot beobtained.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

−1.6<f _(F) /f _(4α)<−0.7  (6)

where,

f_(F) is a focal length of the focusing lens unit, and

f_(4α) is a composite focal length of the fourth lens unit and a lensunit subsequent thereto at a wide-angle limit.

The condition (6) sets forth the ratio between the focal length of thefocusing lens unit and the composite focal length of the fourth lensunit and a lens unit subsequent thereto. When the value exceeds theupper limit of the condition (6), the fluctuation in the field curvatureat the time of focusing increases. Thus, this situation is unpreferable.Further, when the value goes below the lower limit of the condition (6),it may cause upsizing of the optical system when the amount of movementin association with focusing is large. Thus, this situation isunpreferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

12<f ₁*(f _(T) /f _(W))/√(f _(W) *f _(T))<27  (7)

where,

f₁ is a focal length of the first lens unit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (7) sets forth the relation between the focal length ofthe first lens unit and the focal length of the entire system. When thevalue exceeds the upper limit of the condition (7), it causes anincrease in the amount of movement of the first unit from a wide-anglelimit to a telephoto limit, and as a result, an intersection angle(pressure angle) of the cam become acute, resulting in fluctuation inload of the cam. Thus, this situation is unpreferable. Further, when thevalue goes below the lower limit of the condition (7), it becomesdifficult to compensate the magnification chromatic aberration generatedin the first lens unit by using the subsequent lens units. Thus, thissituation is unpreferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

−20<f ₂*(f _(T) /f _(W))/√(f _(W) *f _(T))<−6  (8)

where,

f₂ is a focal length of the second lens unit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (8) sets forth the relation between the focal length ofthe second lens unit and the focal length of the entire system. When thevalue exceeds the upper limit of the condition (8), the negative opticalpower of the second lens unit is excessively increased, and the fieldcurvature is apt to be toward the under side, and as a result, thedifference in the peripheral image surface increases between thewide-angle limit and the telephoto limit at the time of variation ofmagnification. Thus, the situation is not preferable. Further, when thevalue goes below the lower limit of the condition (8), the negativeoptical power of the second lens unit is excessively decreased, and thefield curvature is apt to be toward the over side, and as a result, thedifference in the peripheral image surface increases between thewide-angle limit and the telephoto limit at the time of variation ofmagnification. Thus, this situation is not preferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

0.5<δt ₁ /f ₁<1.1  (9)

where,

δt₁ is an amount of movement of the first lens unit from a wide-anglelimit to a telephoto limit (where, the position of the wide-angle limitis set as the reference, and expansion to the object side from thereference position is regarded as a positive value), and

f₁ is a focal length of the first lens unit.

The condition (9) sets forth the amount of movement of the first lensunit in the optical axis direction. When the value exceeds the upperlimit of the condition (9), with a moving mechanism of the first lensunit being configured with a cam, it is difficult to smoothly form thecurve of the cam groove. When the value of the condition (9) goes belowthe lower limit, the overall length is elongated at a wide-angle limit,or the overall length is shortened at a telephoto limit. When theoverall length is elongated at a wide-angle limit, a front lens diameterincreases. Thus, this is unpreferable. On the other hand, when theoverall length is shortened at a telephoto limit, the sensitivity of thefirst lens unit increases. This situation is unpreferable from theviewpoint of manufacturing.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

−0.7<δt ₂ /f ₂<−0.2  (10)

where,

δt₂ is an amount of movement of the second lens unit from a wide-anglelimit to a telephoto limit (where, the position of the wide-angle limitis set as the reference, and expansion to the object side from thereference position is regarded as a positive value), and

f₂ is a focal length of the second lens unit.

The condition (10) sets forth the amount of movement of the second lensunit in the optical axis direction. When the value exceeds the upperlimit of the condition (10), the position of the incident pupil movesconsiderably deeply to the image surface side, which causes increase inthe front lens diameter. Thus, this situation is unpreferable. Further,when the value goes below the lower limit of the condition (10), thepower of the second lens unit increases, and this causes difficulty incompensating aberration. If the aberration compensation is to beperformed, the number of lenses will be increased. Thus, this situationis unpreferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

−1.2<δt ₃ /f ₃<−0.4  (11)

where,

δt₃ is an amount of movement of the third lens unit from a wide-anglelimit to a telephoto limit (where, the position of the wide-angle limitis set as the reference, and expansion to the object side from thereference position is regarded as a positive value), and

f₃ is a focal length of the third lens unit.

The condition (11) sets forth the amount of movement of the third lensunit in the optical axis direction. When the value exceeds the upperlimit of the condition (11), upsizing of the actuator for focusing willbe caused. Thus, this situation is unpreferable. Further, when the valuegoes below the lower limit of the condition (11), the power of the thirdlens unit increases, and sensitivity for decentering increases. Thus,this situation is unpreferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

1.2<δt ₄ /f ₄<2.0  (12)

where,

δt₄ is an amount of movement of the fourth lens unit from a wide-anglelimit to a telephoto limit (where, the position of the wide-angle limitis set as the reference, and expansion to the object side from thereference position is regarded as a positive value), and

f₄ is a focal length of the fourth lens unit.

The condition (12) sets forth the amount of movement of the fourth lensunit in the optical axis direction. When the value exceeds the upperlimit of the condition (12), the overall length of the entire system iselongated at a telephoto limit, and thus the amount of movement of thefirst lens unit from a wide-angle limit to a telephoto limit increases.When a moving mechanism of the first lens unit is configured with a cam,the intersection angle (pressure angle) of the cam becomes acute,resulting in fluctuation in load of the cam. Thus, this situation isunpreferable. Further, when the value goes below the lower limit of thecondition (12), the power of the second lens unit increases, andfluctuation in the field curvature increases from a wide-angle limit toa telephoto limit, which cause difficulty in its compensation. Thus,this situation is unpreferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

−25<β_(2T)/β_(2W)<34  (13)

where,

β_(2T) is paraxial imaging magnification of the second lens unit at atelephoto limit, and

β_(2W) is paraxial imaging magnification of the second lens unit at awide-angle limit.

The condition (13) sets forth the change in magnification of the secondlens unit. When the value exceeds the upper limit of the condition (13),it becomes difficult to compensate aberration from a wide-angle limit toa telephoto limit. Thus, this situation is unpreferable. Further, whenthe value goes below the lower limit of the condition (13), the amountof movement of the second lens unit from a wide-angle limit to atelephoto limit increases, and consequently, the overall length of theentire system is elongated. Thus, this situation is unpreferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

−8<β_(3T)/β_(3W)<0.2  (14)

where,

β_(3T) is paraxial imaging magnification of the third lens unit at atelephoto limit, and

β_(3W) is paraxial imaging magnification of the third lens unit at awide-angle limit.

The condition (14) sets forth the change in magnification of the thirdlens unit. When the value exceeds the upper limit of the condition (14),the power of the third lens unit is increased, and fluctuation of animage at the time of focusing increases. Thus, this situation isunpreferable. Further, when the value goes below the lower limit of thecondition (14), the power of the third lens unit is decreased, theamount of movement of the third lens unit at the time of focusingincreases. Thus, this situation is unpreferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

2<β_(4T)/β_(4W)<3.2  (15)

where,

β_(4T) is paraxial imaging magnification of the fourth lens unit at atelephoto limit, and

β_(4W) is paraxial imaging magnification of the fourth lens unit at awide-angle limit.

The condition (15) sets forth the change in magnification of the fourthlens unit. When the value exceeds the upper limit of the condition (15),the incident angle of light to be incident on the image surface at awide-angle limit increases, and it becomes difficult to maintain thetelecentricity. Thus, this situation is unpreferable. Further, when thevalue goes below the lower limit of the condition (15), the back focusis elongated at a wide-angle limit, and the entire system cannot becompact. Thus, this situation is unpreferable.

If the focusing lens unit included in the zoom lens system according toeach embodiment has an aspheric surface, it is preferable that thefollowing condition is satisfied.

−0.3<f _(F)*β_(FW)*β_(FW)/(δs _(F) *f _(T) /f _(W))<7.0  (16)

where,

f_(F) is a focal length of the focusing lens unit,

β_(FW) is paraxial imaging magnification of the focusing lens unit at awide-angle limit,

δs_(F) is an amount of deformation of an aspheric surface at a height of0.5*f_(W)*tan ω_(W) from the optical axis, the aspheric surface beingarranged closest to the object side in the focusing lens unit,

f_(T) is a focal length of the entire system at a telephoto limit,

f_(W) is a focal length of the entire system at a wide-angle limit, and

ω_(W) is a half view angle at a wide-angle limit.

The condition (16) sets forth the relation between the paraxial imagingmagnification and the amount of aspheric aberration of the focusing lensunit. When the value exceeds the upper limit of the condition (16), theastigmatism and spherical aberration from an infinity distance at atelephoto limit to a close-point distance are increased to the underside, and thus this situation is unpreferable from the viewpoint of theaberration compensation. When the value goes below the lower limit ofthe condition (16), the aberration sensitivity relative to processerrors increases, and thus fluctuation in the field curvature caused bymanufacturing variation increases. Thus, this situation is unpreferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

−1.7<DIS _(W) *f _(T) /f _(W)<−0.5  (17)

where,

DIS_(W) is an amount of distortion of the maximum image height at awide-angle limit,

f_(T) is a focal length of the entire system at a telephoto limit, and

f_(W) is a focal length of the entire system at a wide-angle limit.

The condition (17) sets forth the relation between the amount ofdistortion and a variable magnification ratio. In the case whre thecamera system is provided with a distortion compensation system, whenthe value exceeds the upper limit of the condition (17), the advantageof shortening of the overall length by the above system cannot beutilized. Thus, this situation is unpreferable. In contrast, when thevalue goes below the lower limit of the condition (17), the imagemagnification rate is increased in the distortion compensation process,resulting in degradation in resolution. Thus, this situation isunpreferable.

In the zoom lens system according to each embodiment, it is preferablethat the following condition is satisfied.

1.88<nd₂  (18)

where,

nd₂ is an average refractive index of a lens element (a portionexcluding a resin layer in the case of a hybrid lens) included in thesecond lens unit.

When the value goes below the lower limit of the condition (18), thedistortion mainly at a wide-angle limit increases due to decrease in thecurvature of the lens, which causes difficulty in compensating theaberration. Thus, this situation is unpreferable.

Here, the individual lens units included in the zoom lens systemaccording to each embodiment may be composed exclusively of refractivetype lens elements that deflect incident light by refraction (that is,lens elements of a type in which deflection is achieved at the interfacebetween media each having a distinct refractive index). Alternatively,the lens may be composed of any one of, or a combination of some of:diffractive type lens elements that deflect the incident light bydiffraction; refractive-diffractive hybrid type lens elements thatdeflect the incident light by a combination of diffraction andrefraction; refractive index distribution type lens elements thatdeflect the incident light by distribution of refractive index in themedium, and the like.

Embodiment 7

FIG. 19 is a schematic construction diagram of a camera system accordingto Embodiment 7.

A camera system 100 according to the present embodiment includes acamera body 101, and an interchangeable lens apparatus 201 connected tothe camera body 101 in an attachable and removable manner.

The camera body 101 includes an image sensor 102 which receives anoptical image formed by a zoom lens system 202 of the interchangeablelens apparatus 201 thereby to convert the optical image into an electricimage signal, a liquid crystal display monitor 103 which displays animage signal converted by the image sensor 102, and a camera mountsection 104. On the other hand, the interchangeable lens apparatus 201includes the zoom lens system 202 according to any one of Embodiments 1to 6, a lens barrel which holds the zoom lens system 202, and a lensmount section 204 connected to the camera mount section 104 of thecamera body. The camera mount section 104 and the lens mount section 204are connected to each other not only physically but also electrically,and function as interfaces. That is, a controller (not shown) inside thecamera body 101 is electrically connected to a controller (not shown)inside the interchangeable lens apparatus 201, thereby achieving mutualsignal communication.

The camera system 100 according to the present embodiment includes thezoom lens system 202 according to any one of Embodiments 1 to 6, andhence is capable of displaying an preferable optical image at the timeof focusing in a live view state.

EXAMPLES

Hereinafter, numerical examples will be described below in which thezoom lens systems according to Embodiments 1 to 6 are implementedspecifically. As will be described later, Numerical Examples 1 to 6corresponds to Embodiments 1 to 6, respectively. Here, in each numericalexample, the units of the length are all “mm”, while the units of theview angle are all “°”. Moreover, in the numerical examples, r is theradius of curvature, d is the axial distance, nd is the refractive indexto the d-line, and vd is the Abbe number to the d-line. In the numericalexamples, the surfaces marked with “*” are aspheric surfaces, and theaspheric surface configuration is defined by the following formula.

$Z = {\frac{h^{2}/r}{1 + \sqrt{1 - {\left( {1 + \kappa} \right)\left( {h/r} \right)^{2}}}} + {\sum\; {A_{n}h^{n}}}}$

Here, the symbols in the formula indicate the following quantities:Z is the distance from an on-the-aspheric-surface point at a height hrelative to the optical axis to a tangential plane at the top of theaspheric surface;h is the height relative to the optical axis;r is the radius of curvature at the top;κ is the conic constant; andA_(n) is the n-th order aspheric coefficient.

FIGS. 2, 5, 8, 11, 14, and 17 are longitudinal aberration diagrams of aninfinity in-focus condition of the zoom lens systems according toNumerical Examples 1, 2, 3, 4, 5, and 6.

In each longitudinal aberration diagram, part (a) shows the aberrationat a wide-angle limit, part (b) shows the aberration at a middleposition, and part (c) shows the aberration at a telephoto limit. Eachlongitudinal aberration diagram, in order from the left-hand side, showsthe spherical aberration (SA (mm)), the astigmatism (AST (mm)), and thedistortion (DIS (%)). In each spherical aberration diagram, the verticalaxis indicates the F-number (in each diagram, indicated as F), the solidline, the short dash line, and the long dash line indicate thecharacteristics to the d-line, the F-line, and the C-line, respectively.In each astigmatism diagram, the vertical axis indicates the imageheight (in each diagram, indicated as H), the solid line and the dashline indicate the characteristics to the sagittal image plane (in eachdiagram, indicated as “s”) and the meridional image plane (in eachdiagram, indicated as “m”), respectively. In each distortion diagram,the vertical axis indicates the image height (in each diagram, indicatedas H).

FIGS. 3, 6, 9, 12, 15, and 18 are lateral aberration diagrams in a basicstate where image blur compensation is not performed and in an imageblur compensation state of a zoom lens system according to NumericalExamples 1, 2, 3, 4, 5 and 6.

In each lateral aberration diagram, the aberration diagrams in the upperthree parts correspond to a basic state where image blur compensation isnot performed at a telephoto limit, while the aberration diagrams in thelower three parts correspond to an image blur compensation state at atelephoto limit where the sub lens unit (first sub lens unit or secondsub lens unit) for image blur compensation included in the fourth lensunit G4 moves by a predetermined amount in a direction perpendicular tothe optical axis. Among the lateral aberration diagrams of a basicstate, the upper part shows the lateral aberration at an image point of70% of the maximum image height, the middle part shows the lateralaberration at the axial image point, and the lower part shows thelateral aberration at an image point of −70% of the maximum imageheight. Among the lateral aberration diagrams of an image blurcompensation state, the upper part shows the lateral aberration at animage point of 70% of the maximum image height, the middle part showsthe lateral aberration at the axial image point, and the lower partshows the lateral aberration at an image point of −70% of the maximumimage height. Further, in each lateral aberration diagram, thehorizontal axis indicates the distance from the principal ray on thepupil surface, and the solid line, the short dash line, and the longdash line indicate the characteristics to the d-line, the F-line, andthe C-line, respectively. In each lateral aberration diagram, themeridional image plane is adopted as the plane containing the opticalaxis of the first lens unit G1.

Here, in the zoom lens system according to each numerical example, theamount (Y_(T)(mm)) of movement of the compensation lens unit in adirection perpendicular to the optical axis in an image blurcompensation state at a telephoto limit is as follows.

TABLE 1 (Amount of movement of compensation lens unit) Numerical ExampleY_(T) 1 0.307 2 0.316 3 0.319 4 0.135 5 0.307 6 0.304

Numerical Example 1

The zoom lens system of Numerical Example 1 corresponds to Embodiment 1shown in FIG. 1. Data of the zoom lens system according to NumericalExample 1, i.e., the surface data, the aspheric surface data, thevarious data, the lens element data, the zoom lens unit data, and thezoom lens unit magnification are shown in Table 2, Table 3, Table 4,Table 5, Table 6, and Table 7, respectively.

TABLE 2 (Surface data) Surface number r d nd vd Object surface ∞  193.29160 1.49730 1.84666 23.8  2 50.82680 7.10180 1.49700 81.6  3−850.01520 0.15000  4 47.79330 5.18430 1.71300 53.9  5 149.47070Variable  6* 76.05160 0.10000 1.51358 51.6  7 53.79460 1.10000 1.8830040.8  8 11.90020 6.30730  9 −20.07120 0.83030 1.88300 40.8 10 −51.308700.87050 11 31.52170 3.39400 1.94595 18.0 12 −51.59310 Variable 13*−19.66880 1.20040 1.80470 41.0 14* 129.88760 Variable 15 (Diaphragm) ∞0.84560 16* 23.65630 3.02980 1.69350 53.2 17* −55.43650 2.59200 1815.08640 3.25030 1.71300 53.9 19 −200.75790 0.81020 2.00069 25.5 2015.26070 1.91050 21 31.27490 5.91480 1.59201 67.0 22* −20.38770 0.8991023 88.68500 2.96870 1.80518 25.5 24 −13.73040 0.80000 1.83481 42.7 2516.65510 2.35020 26 23.27780 4.19350 1.49700 81.6 27 −14.99240 0.800001.83481 42.7 28 −57.80160 1.35890 29 −14.16000 0.80000 1.72916 54.7 30−26.58250 0.10000 31 32.36170 3.20070 1.51680 64.2 32 −81.55460 Variable33 ∞ 4.20000 1.51680 64.2 34 ∞ BF image surface ∞

TABLE 3 (Aspheric surface data) Surface No. Parameters 6 K =−9.51780E−01, A4 = 2.71746E−05, A6 = −1.19865E−08, A8 = −8.37911E−10,A10 = 5.57759E−12, A12 = −1.15782E−14 13 K = 0.00000E+00, A4 =−3.91729E−05, A6 = 1.79189E−06, A8 = −3.13080E−08, A10 = 1.39737E−10,A12 = 2.27477E−12 14 K = −1.79163E−01, A4 = −4.45555E−05, A6 =2.19191E−06, A8 = −5.22554E−08, A10 = 5.17499E−10, A12 = −1.04173E−13 16K = 0.00000E+00, A4 = −1.12821E−05, A6 = 1.40905E−07, A8 = −2.71306E−09,A10 = −7.19478E−11, A12 = −7.19829E−15 17 K = 0.00000E+00, A4 =2.44778E−05, A6 = −3.84078E−08, A8 = 1.18435E−09, A10 = −1.10289E−10,A12 = 7.33811E−15 22 K = 0.00000E+00, A4 = 1.81139E−05, A6 =−5.84158E−08, A8 = 6.50501E−09, A10 = −6.84134E−11, A12 = 0.00000E+00

TABLE 4 (Various data) Zooming ratio 9.33675 Wide Middle Telephoto Focallength 14.4919 44.3151 135.3070 F-number 4.00318 5.40622 5.99766 Viewangle 39.8611 13.7123 4.5845 Image height 10.8150 10.8150 10.8150Overall length of lens 101.9455 132.7027 162.8905 system BF 2.805492.83204 2.87020 d5 0.6596 22.5410 41.6141 d12 2.8371 3.0868 6.1035 d1418.4343 8.8238 2.7427 d32 9.4488 27.6589 41.7998 Entrance pupil position25.3181 78.7228 223.8111 Exit pupil position −37.3774 −55.5875 −69.7284Front principal point 34.5835 89.4220 106.9372 position Back principalpoint 87.4536 88.3877 27.5835 position

TABLE 5 (Lens element data) Unit Initial surface No. Focal length 1 1−134.0520 2 2 96.7509 3 4 96.4914 4 6 −16.6778 5 9 −37.8072 6 11 21.10407 13 −21.1522 8 16 24.2899 9 18 19.8043 10 19 −14.1462 11 21 21.7746 1223 14.9598 13 24 −8.9085 14 26 19.0411 15 27 −24.4565 16 29 −42.7154 1731 45.2638

TABLE 6 (Zoom lens unit data) Initial Length Front surface Focal of lensprincipal Back principal Unit No. length unit point position pointposition 1 1 76.72300 13.93340 3.26962 8.46360 2 6 −46.93302 12.60210−10.83666 −15.28913 3 13 −21.15218 1.20040 0.08717 0.62478 4 15 19.3777235.82430 0.10418 10.76940

TABLE 7 (Zoom lens unit magnification) Initial surface Unit No. WideMiddle Telephoto 1 1 0.00000 0.00000 0.00000 2 6 −1.36049 −3.720167.26826 3 13 0.12997 0.07727 −0.08852 4 15 −1.06826 −2.00938 −2.74110

Numerical Example 2

The zoom lens system of Numerical Example 2 corresponds to Embodiment 2shown in FIG. 4. Data of the zoom lens system of Numerical Example 2,i.e., the surface data, the aspheric surface data, the various data, thelens element data, the zoom lens unit data, and the zoom lens unitmagnification are shown in Tables 8, 9, 10, 11, 12, and 13,respectively.

TABLE 8 (Surface data) Surface number r d nd vd Object surface ∞  192.44320 1.50040 1.84666 23.8  2 50.47000 6.96430 1.49700 81.6  3−847.86000 0.15000  4 47.25220 5.18030 1.71300 53.9  5 145.99490Variable  6* 76.11200 0.10120 1.51358 51.6  7 53.78650 1.10000 1.8830040.8  8 11.89720 6.31220  9 −19.99880 0.83260 1.88300 40.8 10 −51.235800.87230 11 31.55930 3.41140 1.94595 18.0 12 −51.41040 Variable 13*−19.63500 1.20060 1.80470 41.0 14* 130.38440 Variable 15 (Diaphragm) ∞0.84590 16* 23.66010 3.04770 1.69350 53.2 17* −55.50020 2.53870 1815.07960 3.25040 1.71300 53.9 19 −200.13220 0.81020 2.00069 25.5 2015.26060 1.91230 21 31.28720 5.87150 1.59201 67.0 22* −20.38280 0.8991023 88.69790 2.96860 1.80518 25.5 24 −13.74920 0.80050 1.83481 42.7 2516.65470 2.35520 26 23.28540 4.19220 1.49700 81.6 27 −15.00380 0.806601.83481 42.7 28 −57.73780 1.34160 29 −14.16980 0.82280 1.72916 54.7 30−26.59680 0.14240 31 32.16560 3.16330 1.51680 64.2 32 −83.11460 Variable33 ∞ 4.20000 1.51680 64.2 34 ∞ BF Image surface ∞

TABLE 9 (Aspherical data) Surface No. Parameters 6 K = −8.65420E−01, A4= 2.71985E−05, A6 = −1.27416E−08, A8 = −8.47671E−10, A10 = 5.59117E−12,A12 = −1.03453E−14 13 K = 0.00000E+00, A4 = −3.92219E−05, A6 =1.79165E−06, A8 = −3.13018E−08, A10 = 1.39699E−10, A12 = 2.24266E−12 14K = 5.23028E−01, A4 = −4.45154E−05, A6 = 2.19210E−06, A8 = −5.22781E−08,A10 = 5.16605E−10, A12 = −1.29893E−13 16 K = 0.00000E+00, A4 =−1.12931E−05, A6 = 1.40885E−07, A8 = −2.71412E−09, A10 = −7.20168E−11,A12 = −9.67929E−15 17 K = 0.00000E+00, A4 = 2.44916E−05, A6 =−3.83424E−08, A8 = 1.18545E−09, A10 = −1.10236E−10, A12 = 9.17521E−15 22K = 4.76603E−05, A4 = 1.81709E−05, A6 = −5.78282E−08, A8 = 6.49528E−09,A10 = −6.93375E−11, A12 = 0.00000E+00

TABLE 10 (Various data) Zooming ratio 9.35820 Wide Middle TelephotoFocal length 14.4939 44.3129 135.6373 F-number 4.00335 5.40554 5.99765View angle 39.9177 13.7265 4.5757 Image height 10.8150 10.8150 10.8150Overall length of lens 101.6672 132.4129 161.5468 system BF 2.804092.82823 2.86170 d5 0.6595 22.4493 41.6494 d12 2.6575 3.0940 6.3380 d1418.4611 8.8422 2.7298 d32 9.4907 27.6049 40.3736 Entrance pupil position25.1796 78.8630 230.4632 Exit pupil position −37.4743 −55.5885 −68.3572Front principal point 34.4580 89.5616 107.7774 position Back principalpoint 87.1732 88.1000 25.9095 position

TABLE 11 (Lens element data) Unit Initial surface No. Focal length 1 1−133.4756 2 2 96.0920 3 4 95.8923 4 6 −16.6715 5 9 −37.6192 6 11 21.09417 13 −21.1314 8 16 24.3029 9 18 19.7920 10 19 −14.1429 11 21 21.7676 1223 14.9778 13 24 −8.9151 14 26 19.0518 15 27 −24.4932 16 29 −42.7860 1731 45.2974

TABLE 12 (Zoom lens unit data) Initial Length Front surface Focal oflens principal Back principal Unit No. length unit point position pointposition 1 1 76.12978 13.79500 3.16804 8.32000 2 6 −46.72192 12.62970−10.78714 −15.22577 3 13 −21.13139 1.20060 0.08676 0.62446 4 15 19.4038735.76900 0.15790 10.71360

TABLE 13 (Zoom lens unit magnification) Initial surface Unit No. WideMiddle Telephoto 1 1 0.00000 0.00000 0.00000 2 6 −1.37173 −3.807606.74257 3 13 0.13000 0.07635 −0.09926 4 15 −1.06759 −2.00237 −2.66214

Numerical Example 3

The zoom lens system of Numerical Example 3 corresponds to Embodiment 3shown in FIG. 7. Data of the zoom lens system of Numerical Example 3,i.e., the surface data, the aspheric surface data, the various data, thelens element data, the zoom lens unit data, and the zoom lens unitmagnification are shown in Tables 14, 15, 16, 17, 18, and 19,respectively.

TABLE 14 (Surface data) Surface number r d nd vd Object surface ∞  187.57360 1.50040 1.84666 23.8  2 49.16650 5.95510 1.49700 81.6  3−2809.37530 0.15000  4 47.74460 4.98760 1.71300 53.9  5 153.09470Variable  6* 73.99720 0.10000 1.51358 51.6  7 52.32450 1.10000 1.8830040.8  8 11.87980 6.08650  9 −19.94860 0.80350 1.88300 40.8 10 −51.953400.84480 11 29.62330 2.59210 1.94595 18.0 12 −56.59100 Variable 13*−19.86560 1.20660 1.80420 46.5 14* 121.10780 Variable 15 (Diaphragm) ∞0.81880 16* 23.31780 2.36020 1.69400 56.3 17* −61.41970 1.01400 1814.71050 3.27940 1.71300 53.9 19 −214.88630 0.84300 2.00069 25.5 2015.15610 1.61840 21 29.47780 4.92500 1.59201 67.0 22* −21.29430 0.9414023 84.78160 3.00080 1.80519 25.4 24 −13.99680 0.83390 1.83481 42.7 2516.54600 1.65990 26 22.59390 4.20830 1.49700 81.6 27 −15.32610 0.800001.83481 42.7 28 −61.45340 1.49380 29 −15.39840 0.80000 1.72600 53.4 30−31.40970 0.10000 31 36.45700 2.50420 1.51633 64.0 32 −64.85300 Variable33 ∞ 4.20000 1.51680 64.2 34 ∞ BF Image surface ∞

TABLE 15 (Aspheric surface data) Surface No. Parameters 6 K =−4.63021E+00, A4 = 2.48887E−05, A6 = −8.40845E−08, A8 = −7.99164E−10,A10 = 8.24811E−12, A12 = −1.11332E−14 13 K = 0.00000E+00, A4 =−4.90964E−05, A6 = 1.59884E−06, A8 = −3.80642E−08, A10 = 1.89425E−11,A12 = 6.27292E−12 14 K = −4.80635E+01, A4 = −4.73983E−05, A6 =1.93516E−06, A8 = −5.59716E−08, A10 = 5.06744E−10, A12 = 7.60511E−13 16K = 0.00000E+00, A4 = −8.98901E−06, A6 = 1.86825E−07, A8 = −2.18893E−09,A10 = −6.51294E−11, A12 = −7.88436E−14 17 K = 0.00000E+00, A4 =2.49414E−05, A6 = −5.17973E−08, A8 = 1.07578E−09, A10 = −1.09559E−10,A12 = 2.62430E−13 22 K = 0.00000E+00, A4 = 3.00044E−05, A6 =9.15117E−08, A8 = 7.25391E−09, A10 = −7.93499E−11, A12 = 0.00000E+00

TABLE 16 (Various data) Zooming ratio 9.74613 Wide Middle TelephotoFocal length 13.8816 44.3100 135.2916 F-number 4.00307 5.40538 5.99705View angle 43.0929 13.7615 4.5780 Image height 10.8150 10.8150 10.8150Overall length of lens 95.0223 125.9994 155.4293 system BF 10.6914910.71602 10.74727 d5 0.6598 22.7406 41.7210 d12 2.0929 3.2189 7.1676 d1418.9120 8.7968 2.7269 d32 1.9384 19.7994 32.3388 Entrance pupil position23.9379 78.2752 229.2315 Exit pupil position −25.6011 −43.4621 −56.0015Front principal point 32.5099 86.3459 90.3034 position Back principalpoint 81.1407 81.6894 20.1377 position

TABLE 17 (Lens element data) Unit Initial surface No. Focal length 1 1−134.8246 2 2 97.2929 3 4 95.4300 4 6 −16.7536 5 9 −37.1102 6 11 20.86077 13 −21.1407 8 16 24.6347 9 18 19.4254 10 19 −14.1219 11 21 21.6649 1223 15.1251 13 24 −8.9715 14 26 19.0767 15 27 −24.6532 16 29 −42.5012 1731 45.5830

TABLE 18 (Zoom lens unit data) Initial Length Front surface Focal oflens principal Back principal Unit No. length unit point position pointposition 1 1 76.29653 12.59310 2.55334 7.29477 2 6 −44.71579 11.52690−9.49042 −13.10859 3 13 −21.14067 1.20660 0.09388 0.63425 4 15 18.4716531.20110 −0.89867 9.45045

TABLE 19 (Zoom lens unit magnification) Initial surface Unit No. WideMiddle Telephoto 1 1 0.00000 0.00000 0.00000 2 6 −1.27348 −3.431177.51757 3 13 0.14129 0.08551 −0.08868 4 15 −1.01117 −1.97943 −2.65997

Numerical Example 4

The zoom lens system of Numerical Example 4 corresponds to Embodiment 4shown in FIG. 10. Data of the zoom lens system of Numerical Example 4,i.e., the surface data, the aspheric surface data, the various data, thelens element data, the zoom lens unit data, and the zoom lens unitmagnification are shown in Tables 20, 21, 22, 23, 24, and 25.

TABLE 20 (Surface data) Surface number r d nd vd Object surface ∞  192.18470 1.50890 1.84666 23.8  2 50.59720 7.14140 1.49700 81.6  3−966.46410 0.15000  4 47.41520 5.21930 1.71300 53.9  5 147.10900Variable  6* 76.06950 0.10000 1.51358 51.6  7 53.68590 1.10000 1.8830040.8  8 11.89330 6.30890  9 −20.09130 0.82990 1.88300 40.8 10 −51.394200.86980 11 31.43820 3.39610 1.94595 18.0 12 −51.92400 Variable 13*−19.67220 1.20030 1.80470 41.0 14* 130.03760 Variable 15 (Diaphragm) ∞0.84510 16* 23.65970 3.08600 1.69350 53.2 17* −55.55620 2.52620 1815.07550 3.25020 1.71300 53.9 19 −200.60280 0.81020 2.00069 25.5 2015.26000 1.91520 21 31.28380 5.89510 1.59201 67.0 22* −20.38310 0.8997023 88.64240 2.96970 1.80518 25.5 24 −13.75430 0.80000 1.83481 42.7 2516.65230 2.34540 26 23.28500 4.18950 1.49700 81.6 27 −14.99040 0.800001.83481 42.7 28 −57.73810 1.34500 29 −14.15720 0.80000 1.72916 54.7 30−26.59940 0.12110 31 32.21740 3.16040 1.51680 64.2 32 −82.24800 Variable33 ∞ 4.20000 1.51680 64.2 34 ∞ BF Image surface ∞

TABLE 21 (Aspheric surface data) Sur- face No. Parameters 6 K =−9.10525E−01, A4 = 2.71853E−05, A6 = −1.17499E−08, A8 = −8.46191E−10,A10 = 5.58176E−12, A12 = −1.05149E−14 13 K = 0.00000E+00, A4 =−3.91920E−05, A6 = 1.79159E−06, A8 = −3.13204E−08, A10 = 1.39427E−10,A12 = 2.21441E−12 14 K = 2.72517E−01, A4 = −4.45295E−05, A6 =2.19143E−06, A8 = −5.22877E−08, A10 = 5.16656E−10, A12 = −5.67168E−14 16K = 0.00000E+00, A4 = −1.12941E−05, A6 = 1.40911E−07, A8 = −2.71164E−09,A10 = −7.19359E−11, A12 = −5.77241E−15 17 K = 0.00000E+00, A4 =2.44934E−05, A6 = −3.84036E−08, A8 = 1.18226E−09, A10 = −1.10332E−10,A12 = 5.60567E−15 22 K = 0.00000E+00, A4 = 1.81820E−05, A6 =−5.77336E−08, A8 = 6.49279E−09, A10 = −6.93404E−11, A12 = 0.00000E+00

TABLE 22 (Various data) Zooming ratio 9.33034 Wide Middle TelephotoFocal length 14.5015 44.3144 135.3042 F-number 4.00344 5.40547 5.99782View angle 39.8346 13.7288 4.5866 Image height 10.8150 10.8150 10.8150Overall length of lens 101.9638 132.5433 161.6026 system BF 2.801902.83011 2.85362 d5 0.6873 22.4396 41.7186 d12 2.7417 3.0466 6.0472 d1418.4749 8.8416 2.7452 d32 9.4746 27.6020 40.4546 Entrance pupil position25.4494 78.8584 228.9072 Exit pupil position −37.3528 −55.4802 −68.3328Front principal point 34.7139 89.4949 107.0383 position Back principalpoint 87.4623 88.2289 26.2984 position

TABLE 23 (Lens element data) Unit Initial surface No. Focal length 1 1−134.7090 2 2 96.9672 3 4 96.0367 4 6 −16.6695 5 9 −37.8277 6 11 21.11927 13 −21.1586 8 16 24.3146 9 18 19.7900 10 19 −14.1448 11 21 21.7708 1223 14.9815 13 24 −8.9164 14 26 19.0411 15 27 −24.4618 16 29 −42.6645 1731 45.2195

TABLE 24 (Zoom lens unit data) Initial Length Front surface Focal oflens principal Back principal Unit No. length unit point position pointposition 1 1 76.41416 14.01960 3.24460 8.47258 2 6 −46.76258 12.60470−10.77426 −15.18802 3 13 −21.15864 1.20030 0.08708 0.62466 4 15 19.3824335.75880 0.11636 10.76666

TABLE 25 (Zoom lens unit magnification) Initial surface Unit No. WideMiddle Telephoto 1 1 0.00000 0.00000 0.00000 2 6 −1.36767 −3.759286.83686 3 13 0.13021 0.07704 −0.09712 4 15 −1.06567 −2.00237 −2.66669

Numerical Example 5

The zoom lens system of Numerical Example 5 corresponds to Embodiment 5shown in FIG. 13. Data of the zoom lens system of Numerical Example 5,i.e., the surface data, the aspheric surface data, the various data, thelens element data, the zoom lens unit data, and the zoom lens unitmagnification are shown in Tables 26, 27, 28, 29, 30, and 31,respectively.

TABLE 26 (Surface data) Surface number r d nd vd Object surface ∞  199.13980 2.33470 1.84666 23.8  2 52.37110 6.32020 1.49700 81.6  3−925.21640 0.15000  4 50.90000 6.04860 1.70030 47.8  5 202.89160Variable  6* 152.65080 0.10000 1.51358 51.6  7 100.84460 1.10000 1.8980034.0  8 13.12860 6.11220  9 −20.13630 0.80270 1.88300 40.8 10 −48.430500.81260 11 31.27340 2.98540 1.94595 18.0 12 −72.10650 Variable 13*−22.74160 1.21130 1.69385 53.1 14* 82.01060 Variable 15 (Diaphragm) ∞0.78470 16* 23.93290 2.51070 1.69200 50.6 17* −43.28550 2.32970 1816.54990 3.17420 1.71300 53.9 19 −158.78700 0.80930 2.00069 25.5 2015.49850 1.59880 21 34.82310 6.01540 1.59201 67.0 22* −18.77570 0.8013023 102.39450 2.86260 1.80486 24.7 24 −13.35880 0.81220 1.83481 42.7 2516.79090 2.77270 26 25.43580 4.02130 1.49700 81.6 27 −13.97530 0.800001.83770 42.0 28 −49.24400 1.17460 29 −15.17760 0.80000 1.72600 53.4 30−30.15640 0.54070 31 36.40460 3.43470 1.51680 64.2 32 −61.98770 Variable33 ∞ 4.20000 1.51680 64.2 34 ∞ BF Image surface ∞

TABLE 27 (Aspheric surface data) Sur- face No. Parameters 6 K =−1.52252E+01, A4 = 2.52697E−05, A6 = −5.64467E−08, A8 = −7.35157E−10,A10 = 6.02872E−12, A12 = −1.20876E−14 13 K = 0.00000E+00, A4 =−1.18627E−04, A6 = 3.31215E−06, A8 = −4.98682E−08, A10 = 3.82451E−10,A12 = −1.56034E−12 14 K = −2.46760E+02, A4 = −5.33359E−05, A6 =2.42750E−06, A8 = −4.25379E−08, A10 = 3.50327E−10, A12 = −9.42154E−13 16K = 0.00000E+00, A4 = −1.88639E−05, A6 = −1.68630E−07, A8 =−2.47382E−09, A10 = 8.88812E−12, A12 = −1.49176E−12 17 K = 0.00000E+00,A4 = 2.44994E−05, A6 = −3.99045E−07, A8 = 6.20417E−09, A10 =−1.58881E−10, A12 = −1.93090E−13 22 K = 0.00000E+00, A4 = −1.60567E−06,A6 = 2.26576E−07, A8 = −7.00856E−09, A10 = 7.69602E−11, A12 =0.00000E+00

TABLE 28 (Various data) Zooming ratio 9.35774 Wide Middle TelephotoFocal length 14.4729 44.3138 135.4335 F-number 4.07421 5.46288 6.09784View angle 41.5356 13.7140 4.5535 Image height 10.8150 10.8150 10.8150Overall length of lens 104.5484 133.3466 163.1344 system BF 2.800962.83119 2.86074 d5 0.6600 22.7257 42.6368 d12 4.5590 3.6343 6.6550 d1419.6493 9.2648 2.5625 d32 9.4585 27.4700 40.9988 Entrance pupil position26.6243 79.8886 230.8777 Exit pupil position −38.2148 −56.2263 −69.7551Front principal point 35.9902 90.9515 113.7186 position Back principalpoint 90.0755 89.0328 27.7009 position

TABLE 29 (Lens element data) Unit Initial surface No. Focal length 1 1−134.1927 2 2 99.9445 3 4 95.4590 4 6 −16.4137 5 9 −39.5601 6 11 23.38777 13 −25.5395 8 16 22.6167 9 18 21.1803 10 19 −14.0778 11 21 21.5026 1223 14.8460 13 24 −8.8040 14 26 18.7846 15 27 −23.5370 16 29 −43.0564 1731 44.9134

TABLE 30 (Zoom lens unit data) Initial Length Front surface Focal oflens principal Back principal Unit No. length unit point position pointposition 1 1 78.33422 14.85350 3.25903 8.89267 2 6 −34.33959 11.91290−6.12097 −7.76739 3 13 −25.53954 1.21130 0.15452 0.65407 4 15 20.2240835.24290 0.14983 9.40650

TABLE 31 (Zoom lens unit magnification) Initial surface Unit No. WideMiddle Telephoto 1 1 0.00000 0.00000 0.00000 2 6 −0.78951 −1.60248−22.62201 3 13 0.22929 0.18457 0.02959 4 15 −1.02060 −1.91270 −2.58310

Numerical Example 6

The zoom lens system of Numerical Example 6 corresponds to Embodiment 6shown in FIG. 16. Data of the zoom lens system of Numerical Example6i.e., the surface data, the aspheric surface data, the various data,the lens element data, and the zoom lens unit data, and the zoom lensunit magnification are shown Tables 32, 33, 34, 35, 36, and 37,respectively.

TABLE 32 (Surface data) Surface number r d nd vd Object surface ∞  196.38880 1.83140 1.84666 23.8  2 51.32720 7.17160 1.49700 81.6  3−1041.52250 0.15000  4 50.08330 5.88870 1.71300 53.9  5 179.31700Variable  6* 150.22940 0.10000 1.51358 51.6  7 90.14560 1.10000 1.8830040.8  8 13.06410 6.21440  9 −20.07530 0.80000 1.88300 40.8 10 −49.244900.84260 11 31.56250 3.21200 1.94595 18.0 12 −60.07180 Variable 13*−20.87910 1.20000 1.75550 45.6 14* 104.86010 Variable 15 (Diaphragm) ∞0.81810 16* 23.83230 2.48350 1.69200 50.6 17* −50.69120 2.05850 1815.54500 3.21390 1.71300 53.9 19 −186.00080 0.81070 2.00069 25.5 2015.37050 1.58270 21 32.84490 6.29410 1.59201 67.0 22* −19.63690 0.8563023 93.81100 2.92490 1.80486 24.7 24 −13.60020 0.81520 1.83500 42.7 2516.72890 2.53790 26 23.93100 4.01320 1.49700 81.6 27 −14.58180 0.800001.83500 43.0 28 −54.93540 1.25830 29 −14.78400 0.80000 1.72600 53.4 30−28.74170 0.44170 31 35.76310 3.26860 1.51680 64.2 32 −65.17300 Variable33 ∞ 4.20000 1.51680 64.2 34 ∞ BF Image surface ∞

TABLE 33 (Aspheric surface data) Sur- face No. Parameters 6 K =−6.33103E+00, A4 = 2.69491E−05, A6 = −3.05186E−08, A8 = −6.62321E−10,A10 = 5.86168E−12, A12 = −1.50045E−14 13 K = 0.00000E+00, A4 =−1.05961E−04, A6 = 2.73259E−06, A8 = −4.43877E−08, A10 = 4.92699E−10,A12 = −2.62900E−12 14 K = −3.32156E+02, A4 = −5.95955E−05, A6 =2.15105E−06, A8 = −4.17605E−08, A10 = 6.02623E−10, A12 = −4.39885E−12 16K = 0.00000E+00, A4 = −4.15119E−06, A6 = −7.97858E−09, A8 =−9.21972E−11, A10 = 2.26181E−11, A12 = −4.10250E−14 17 K = 0.00000E+00,A4 = 3.37315E−05, A6 = −1.24287E−07, A8 = 4.05692E−09, A10 =−5.92081E−11, A12 = 5.70665E−13 22 K = 0.00000E+00, A4 = 7.12658E−06, A6= 3.13880E−07, A8 = −7.94374E−09, A10 = 8.71504E−11, A12 = 0.00000E+00

TABLE 34 (Various data) Zooming ratio 9.35203 Wide Middle TelephotoFocal length 14.5073 44.3136 135.6730 F-number 4.01555 5.43865 6.18901View angle 41.1840 13.7525 4.5661 Image height 10.8150 10.8150 10.8150Overall length of lens 103.0175 133.7983 165.7572 system BF 2.799162.83031 2.86280 d5 0.7206 22.7129 42.0552 d12 3.2352 3.8636 7.9752 d1419.1231 9.0032 2.6742 d32 9.4511 27.7000 42.5015 Entrance pupil position26.4439 80.6365 231.6863 Exit pupil position −37.4491 −55.6980 −70.4995Front principal point 35.7221 91.3989 116.4518 position Back principalpoint 88.5101 89.4848 30.0842 position

TABLE 35 (Lens element data) Unit Initial surface No. Focal length 1 1−132.1373 2 2 98.6391 3 4 95.6510 4 6 −16.7330 5 9 −38.8825 6 11 22.25277 13 −22.9529 8 16 23.7497 9 18 20.2551 10 19 −14.1589 11 21 21.7277 1223 14.9396 13 24 −8.8754 14 26 18.8844 15 27 −23.9900 16 29 −42.9688 1731 45.1808

TABLE 36 (Zoom lens unit data) Initial Length Front surface Focal oflens principal Back principal Unit No. length unit point position pointposition 1 1 78.17875 15.04170 3.49155 9.14515 2 6 −40.45795 12.26900−8.30232 −11.16154 3 13 −22.95286 1.20000 0.11304 0.63227 4 15 19.7164534.97760 0.07998 9.82889

TABLE 37 (Zoom lens unit magnification) Initial surface Unit No. WideMiddle Telephoto 1 1 0.00000 0.00000 0.00000 2 6 −1.02670 −2.3233520.97750 3 13 0.17424 0.12419 −0.03045 4 15 −1.03728 −1.96443 −2.71680

The following Tables 38 and 39 show values corresponding to theindividual conditions in the zoom lens systems of the respectivenumerical examples.

TABLE 38 (Corresponding values to individual conditions: NumericalExamples 1 to 5) Numerical Example Condition 1 2 3 4 5 (1) f_(4A)/f_(4α)0.86 0.86 0.85 0.86 0.82 (2) f_(4Ob)/f_(4α) 0.86 0.86 0.85 0.86 0.82 (3)f_(4B)/f_(4α) −1.22 −1.22 −1.29 −1.22 −1.14 (4) f_(4Im)/f_(4α) 4.03 4.004.21 4.02 4.07 (5) f_(4α)/f_(W) 1.34 1.34 1.33 1.34 1.40 (6)f_(F)/f_(4α) −1.09 −1.09 −1.15 −1.09 −1.26 (7) f₁ * (f_(T)/f_(W))/ 16.1916.07 17.17 16.10 16.57 √(f_(W) * f_(T)) (8) f₂ * (f_(T)/f_(W))/ −9.90−9.86 −10.06 −9.86 −7.26 √(f_(W) * f_(T)) (9) δt₁/f₁ 0.79 0.79 0.79 0.780.75 (10) δt₂/f₂ −0.42 −0.40 −0.43 −0.40 −0.48 (11) δt₃/f₃ −0.79 −0.72−0.67 −0.72 −0.57 (12) δt₄/f₄ 1.67 1.59 1.65 1.60 1.56 (13)β_(2T)/β_(2W) −5.34 −4.91 −5.90 −5.00 28.67 (14) β_(3T)/β_(3W) −0.68−0.76 −0.63 −0.75 0.13 (15) β_(4T)/β_(4W) 2.57 2.49 2.63 2.50 2.53 (16)f₃ * β_(3W) * β_(3W)/ 6.21 6.09 1.16 5.99 1.90 (δS₃ * f_(T)/f_(W)) (17)DIS_(W) * f_(T)/f_(W) −1.02 −1.03 −1.55 −1.02 −1.50 (18) nd₂ 1.904 1.9041.904 1.904 1.904

TABLE 39 (Corresponding values to individual conditions: NumericalExamples 6) Numerical Example Conditions 6  (1) f_(4A)/f_(4α) 0.83  (2)f_(4Ob)/f_(4α) 0.83  (3) f_(4B)/f_(4α) −1.19  (4) f_(4Im)/f_(4α) 4.03 (5) f_(4α)/f_(W) 1.36  (6) f_(F)/f_(4α) −1.16  (7) f₁ *(f_(T)/f_(W))/√(f_(W) * f_(T)) 16.49  (8) f₂ * (f_(T)/f_(W))/√(f_(W) *f_(T)) −8.53  (9) δt₁/f₁ 0.80 (10) δt₂/f₂ −0.53 (11) δt₃/f₃ −0.72 (12)δt₄/f₄ 1.68 (13) β_(2T)/β_(2W) −20.42 (14) β_(3T)/β_(3W) −0.17 (15)β_(4T)/β_(4W) 2.62 (16) f₃ * β_(3W) * β_(3W)/(δS₃ * f_(T)/f_(W)) 1.08(17) DIS_(W) * f_(T)/f_(W) −1.40 (18) nd₂ 1.904

The zoom lens system according to the present invention is applicable toa digital input device such as a digital still camera, a digital videocamera, a mobile telephone, a PDA (Personal Digital Assistance), asurveillance camera in a surveillance system, a Web camera or avehicle-mounted camera. In particular, the present zoom lens system issuitable for an imaging device in a digital still camera, a digitalvideo camera or the like that requires high image quality.

Details of the present invention have been described above. However, theabove-mentioned description is completely illustrative from every pointof view, and does not limit the scope of the present invention.Obviously, various improvements and modifications can be performedwithout departing from the scope of the present invention.

1. A zoom lens system comprising a plurality of lens units and anaperture diaphragm arranged in the lens units, and performing zooming bychanging intervals among the lens units, wherein the plurality of lensunits, in order from an object side to an image side, includes: a firstlens unit having positive optical power; a second lens unit havingnegative optical power; a third lens unit having negative optical power;and a fourth lens unit having positive optical power, the aperturediaphragm is arranged on the object side relative to the fourth lensunit so as to be adjacent to the fourth lens unit, and the fourth lensunit includes, in order from the object side to the image side, a lenselement having positive optical power, a lens element having positiveoptical power, and a lens element having negative optical power.
 2. Thezoom lens system as claimed in claim 1, wherein four lens elementsarranged closest to the object side in the fourth lens unit form a sublens unit having positive optical power.
 3. The zoom lens system asclaimed in claim 1, satisfying the following condition:0.6<f _(4Ob) /f _(4α)<1.0  (2) where, when the fourth lens unit, inorder from the object side to the image side, includes; a lens elementhaving positive optical power; a lens element having positive opticalpower; a lens element having negative optical power; and a lens elementhaving positive optical power, f_(4Ob) is a composite focal length ofthe four lens elements, and f_(4α) is a composite focal length of thefourth lens unit and a lens unit subsequent thereto at a wide-anglelimit.
 4. The zoom lens system as claimed in claim 1, satisfying thefollowing condition:−1.6<f _(F)/f_(4α)<−0.7  (6) where, f_(F) is a focal length of afocusing lens unit, and f_(4α) is a composite focal length of the fourthlens unit and a lens unit subsequent thereto at a wide-angle limit. 5.The zoom lens system as claimed in claim 1, satisfying the followingcondition:12<f ₁*(f _(T) /f _(W))/√(f _(W) *f _(T))<27  (7) where, f_(i) is afocal length of the first lens unit, f_(T) is a focal length of anentire system at a telephoto limit, and f_(W) is a focal length of theentire system at a wide-angle limit.
 6. The zoom lens system as claimedin claim 1, satisfying the following condition:−20<f ₂*(f _(T) /f _(W))/√(f _(W) *f _(T))<−6  (8) where, f₂ is a focallength of the second lens unit, f_(T) is a focal length of an entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 7. The zoom lens system as claimed inclaim 1, satisfying the following condition:0.5<δt ₁ /f ₁<1.1  (9) where, δt₁ is an amount of movement of the firstlens unit from a wide-angle limit to a telephoto limit (where, theposition of the wide-angle limit is set as a reference, and expansion tothe object side from the reference position is regarded as a positivevalue), and f₁ is a focal length of the first lens unit.
 8. The zoomlens system as claimed in claim 1, satisfying the following condition:−0.7<δt ₂ /f ₂<−0.2  (10) where, δt₂ is an amount of movement of thesecond lens unit from a wide-angle limit to a telephoto limit (where,the position of the wide-angle limit is set as a reference, andexpansion to the object side from the reference position is regarded asa positive value), and f₂ is a focal length of the second lens unit. 9.The zoom lens system as claimed in claim 1, satisfying the followingcondition:−1.2<δt ₃ /f ₃<−0.4  (11) where, δt₃ is an amount of movement of thethird lens unit from a wide-angle limit to a telephoto limit (where, theposition of the wide-angle limit is set as a reference, and expansion tothe object side from the reference position is regarded as a positivevalue), and f₃ is a focal length of the third lens unit.
 10. The zoomlens system as claimed in claim 1, satisfying the following condition:1.2<δt ₄ /f ₄<2.0  (12) where, δt₄ is an amount of movement of thefourth lens unit from a wide-angle limit to a telephoto limit (where,the position of the wide-angle limit is set as a reference, andexpansion to the object side from the reference position is regarded asa positive value), and f₄ is a focal length of the fourth lens unit. 11.The zoom lens system as claimed in claim 1, satisfying the followingcondition:−25<β_(2T)/β_(2W)<34  (13) where, β_(2T) is paraxial imagingmagnification of the second lens unit at a telephoto limit, and β_(2W)is paraxial imaging magnification of the second lens unit at awide-angle limit.
 12. The zoom lens system as claimed in claim 1,satisfying the following condition:−8<β_(3T)/β_(3W)<0.2  (14) where, β_(3T) is paraxial imagingmagnification of the third lens unit at a telephoto limit, and β_(3W) isparaxial imaging magnification of the third lens unit at a wide-anglelimit.
 13. The zoom lens system as claimed in claim 1, satisfying thefollowing condition:2<β_(4T)/β_(4W)<3.2  (15) where, β_(4T) is paraxial imagingmagnification of the fourth lens unit at a telephoto limit, and β_(4W)is paraxial imaging magnification of the fourth lens unit at awide-angle limit.
 14. The zoom lens system as claimed in claim 1,satisfying the following condition:−0.3<f _(F)*β_(FW)*β_(FW)/(δs _(F) *f _(T) /f _(W))<7.0  (16) where,f_(F) is a focal length of a focusing lens unit, β_(FW) is paraxialimaging magnification of the focusing lens unit at a wide-angle limit,δs_(F) is an amount of distortion of an aspheric surface at a height of0.5*f_(W)*tan ω_(w) from an optical axis, the aspheric surface beingarranged closest to the object side in the focusing lens unit, f_(T) isa focal length of an entire system at a telephoto limit, f_(W) is afocal length of the entire system at a wide-angle limit, and ω_(w) is ahalf view angle at a wide-angle limit.
 15. The zoom lens system asclaimed in claim 1, satisfying the following condition:−1.7<DIS _(W) *f _(T) /f _(W)<−0.5  (17) where, DIS_(w) is an amount ofdistortion of a maximum image height at a wide-angle limit, f_(T) is afocal length of an entire system at a telephoto limit, and f_(W) is afocal length of the entire system at a wide-angle limit.
 16. Aninterchangeable lens apparatus, comprising: a zoom lens system includinga plurality of lens units and an aperture diaphragm arranged in the lensunits, and performing zooming by changing intervals among the lensunits; and a mount section detachably connected to a camera body thatincludes an image sensor which receives an optical image formed by thezoom lens system thereby to convert the optical image to an electricalimage signal, wherein the plurality of lens units, in order from anobject side to an image side, includes: a first lens unit havingpositive optical power: a second lens unit having negative opticalpower; a third lens unit having negative optical power; and a fourthlens unit having positive optical power, the aperture diaphragm isarranged on the object side relative to the fourth lens so as to beadjacent to the fourth lens unit, the fourth lens unit includes, inorder from the object side to the image side, a lens element havingpositive optical power, a lens element having positive optical power,and a lens element having negative optical power.
 17. A camera system,comprising: an interchangeable lens apparatus that includes a zoom lenssystem including a plurality of lens units and an aperture diaphragmarranged in the lens units, and performing zooming by changing intervalsamong the lens units; and a camera body which is connected to theinterchangeable lens apparatus via a camera mount section in anattachable and removable manner and includes an image sensor whichreceives an optical image formed by the zoom lens system thereby toconvert the optical image to an electrical image signal, wherein theplurality of lens units, in order from an object side to an image side,includes: a first lens unit having positive optical power: a second lensunit having negative optical power; a third lens unit having negativeoptical power; and a fourth lens unit having positive optical power, theaperture diaphragm is arranged on the object side relative to the fourthlens so as to be adjacent to the fourth lens unit, the fourth lens unitincludes, in order from the object side to the image side, a lenselement having positive optical power, a lens element having positiveoptical power, and a lens element having negative optical power.
 18. Azoom lens system comprising a plurality of lens units and performingzooming by changing intervals among the lens units, wherein theplurality of lens units, in order from an object side to an image side,includes: a first lens unit having positive optical power: a second lensunit having negative optical power; a third lens unit having negativeoptical power; and a fourth lens unit having positive optical power, thefourth lens unit includes, in order from the image side to the objectside, a lens element having positive optical power, a lens elementhaving negative optical power, a lens element having negative opticalpower, and a lens element having positive optical power.
 19. The zoomlens system as claimed in claim 18, wherein four lens elements arrangedclosest to the image side in the fourth lens unit forms a sub lens unithaving positive optical power.
 20. The zoom lens system as claimed inclaim 18, satisfying the following condition:3.0<f _(4Im) /f _(4α)<4.5  (4) where, when the fourth lens unit, inorder from the image side to the object side, includes; a lens elementhaving positive optical power; a lens element having negative opticalpower; a lens element having negative optical power; and a lens elementhaving positive optical power, f_(4Im) is a composite focal length ofthe four lens elements, and f_(4α) is a composite focal length of thefourth lens unit and a lens unit subsequent thereto at a wide-anglelimit.
 21. The zoom lens system as claimed in claim 18, satisfying thefollowing condition:1.0<f _(4α) /f _(W)<1.5  (5) where, f_(4α) is a composite focal lengthof the fourth lens unit and a lens unit subsequent thereto at awide-angle limit, and f_(W) is a focal length of an entire system at awide-angle limit.
 22. The zoom lens system as claimed in claim 18,satisfying the following condition:−1.6<f _(F) /f _(4α)<−0.7  (6) f_(F) is a focal length of a focusinglens unit, and f_(4α) is a composite focal length of the fourth lensunit and a lens unit subsequent thereto at a wide-angle limit.
 23. Thezoom lens system as claimed in claim 19, satisfying the followingcondition:12<f ₁*(f _(T) /f _(W))/√(f _(W) *f _(T))<27  (7) where, f₁ is a focallength of the first lens unit, f_(T) is a focal length of an entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 24. The zoom lens system as claimed inclaim 18, satisfying the following condition:−20<f ₂*(f _(T) /f _(W))/√(f _(W) *f _(T))<−6  (8) where, f₂ is a focallength of the second lens unit, f_(T) is a focal length of an entiresystem at a telephoto limit, and f_(W) is a focal length of the entiresystem at a wide-angle limit.
 25. The zoom lens system as claimed inclaim 18, satisfying the following condition:0.5<δt ₁ /f ₁<1.1  (9) where, δt₁ is an amount of movement of the firstlens unit from a wide-angle limit to a telephoto limit (where, theposition of the wide-angle limit is set as a reference, and expansion tothe object side from the reference position is regarded as a positivevalue), and f₁ is a focal length of the first lens unit.
 26. The zoomlens system according to claim 18, satisfying the following condition:−0.7<δt ₂ /f ₂<−0.2  (10) where, δt₂ is an amount of movement of thesecond lens unit from a wide-angle limit to a telephoto limit (where,the position of the wide-angle limit is set as a reference, andexpansion to the object side from the reference position is regarded asa positive value), and f₂ is a focal length of the second lens unit. 27.The zoom lens system as claimed in claim 18, satisfying the followingcondition:−1.2<δt ₃ /f ₃<−0.4  (11) where, δt₃ is an amount of movement of thethird lens unit from a wide-angle limit to a telephoto limit (where, theposition of the wide-angle limit is set as a reference, and expansion tothe object side from the reference position is regarded as a positivevalue), and f₃ is a focal length of the third lens unit.
 28. The zoomlens system as claimed in claim 18, satisfying the following condition:1.2<δt ₄ /f ₄<2.0  (12) where, δt₄ is an amount of movement of thefourth lens unit from a wide-angle limit to a telephoto limit (where,the position of the wide-angle limit is set as a reference, andexpansion to the object side from the reference position is regarded asa positive value), and f₄ is a focal length of the fourth lens unit. 29.The zoom lens system as claimed in claim 18, satisfying the followingcondition:−25<β_(2T)/β_(2W)<34  (13) where, β_(2T) is a paraxial imagingmagnification of the second lens unit at a telephoto limit, and β_(2W)is a paraxial imaging magnification of the second lens unit at awide-angle limit.
 30. The zoom lens system as claimed in claim 18,satisfying the following condition:−8<β_(3T)/β_(3W)<0.2  (14) where, β_(3T) is a paraxial imagingmagnification of the third lens unit at a telephoto limit, and β_(3W) isparaxial imaging magnification of the third lens unit at a wide-anglelimit.
 31. The zoom lens system as claimed in claim 18, satisfying thefollowing condition:2<β_(4T)/β_(4W)<3.2  (15) where, β_(4T) is paraxial imagingmagnification of the fourth lens unit at a telephoto limit, and β_(4W)is paraxial imaging magnification of the fourth lens unit at awide-angle limit.
 32. The zoom lens system as claimed in claim 18,satisfying the following condition:−0.3<f _(F)*β_(FW)*β_(FW)/(δs _(F) *f _(T) /f _(W))<7.0  (16) where,f_(F) is a focal length of a focusing lens unit, β_(FW) is paraxialimaging magnification of the focusing lens unit at a wide-angle limit,δs_(F) is an amount of distortion of an aspheric surface at a height of0.5*f_(W)*tan ω_(w) from an optical axis of the aspheric surface locatedclosest to the object side in the focusing lens unit, f_(T) is a focallength of an entire system at a telephoto limit, f_(W) is a focal lengthof the entire system at a wide-angle limit, and ω_(w) is a half viewangle at a wide-angle limit.
 33. The zoom lens system as claimed inclaim 18, satisfying the following condition:−1.7<DIS _(W) *f _(T) /f _(W)<−0.5  (17) where, DIS_(w) is an amount ofdistortion of a maximum image height at a wide-angle limit, f_(T) is afocal length of an entire system at a telephoto limit, and f_(W) is afocal length of the entire system at a wide-angle limit.
 34. Aninterchangeable lens apparatus, comprising: a zoom lens system includinga plurality of lens units, and performing zooming by changing intervalsamong the lens units; and a mount section detachably connected to acamera body that includes an image sensor which receives an opticalimage formed by the zoom lens system thereby to convert the opticalimage to an electric image signal, wherein the plurality of lens units,in order from an object side to an image side, includes: a first lensunit having positive optical power: a second lens unit having negativeoptical power; a third lens unit having negative optical power; and afourth lens unit having positive optical power, the fourth lens unitincludes, in order from the image side to the object side, a lenselement having positive optical power, a lens element having negativeoptical power, a lens element having negative optical power, and a lenselement having positive optical power.
 35. A camera system, comprising:an interchangeable lens apparatus that includes a zoom lens systemincluding a plurality of lens units and performing zooming by changingintervals among the lens units; and a camera body which is connected tothe interchangeable lens apparatus via a camera mount section in anattachable and removable manner and includes an image sensor whichreceives an optical image formed by the zoom lens system thereby toconvert the optical image to an electrical image signal, wherein theplurality of lens units, in order from an object side to an image side,includes: a first lens unit having positive optical power: a second lensunit having negative optical power; a third lens unit having negativeoptical power; and a fourth lens unit having positive optical power, thefourth lens unit includes, in order from the image side to the objectside, a lens element having positive optical power, a lens elementhaving negative optical power, a lens element having negative opticalpower, and a lens element having positive optical power.